1. Technical Field
The present invention pertains to a seat, and particularly to a vehicle seat to be mounted on a vehicle, such as an automobile.
2. Related Art
A vehicle seat to be mounted on a vehicle, such as an automobile, has a structure in which a back part (a seat back) is connected to the rear end part of a seat part (a seat cushion) such that the inclined position thereof is adjustable through a reclining mechanism.
Further, for a vehicle seat, a structure is known which, in order to secure the rigidity of the back part, includes a thick type back part frame. With such a vehicle seat, the back part frame has a high rigidity so that at the time of a collision, impact absorption due to a deformation of the frame is not achieved, i.e., an impact force (acceleration) is transmitted directly to a seated person, without being damped, which may cause damage to the seated person. In addition, with such a vehicle seat, since the back part frame has a high rigidity, vibration absorbing characteristics depend on a cushioning material constituting a backrest provided for the back part frame, and thus it is difficult to obtain good vibration absorbing characteristics.
Further, a vehicle seat, which is provided with a thin type back part frame having a high elasticity, has been developed. In such a vehicle seat, the vibration absorbing characteristics are relatively good, however, if, for example, at the time of a vehicle collision, or the like, a great impact force is applied, the rigidity becomes insufficient, resulting in the possibility that the movement of a seated person due to the inertia cannot be prevented with certainty for protection of the seated person.
In addition, for a vehicle seat, it has been conceived that, in order to alleviate neck damage to a seated person (an occupant), a headrest for restricting the movement of the head of the seated person at the time of a collision (especially a rear collision), or the like, is positively moved to the head side to suppress the amount of movement of the head (for example, referring to patent document 1 to patent document 3).
In the patent document 1, an automobile seat is disclosed which has a structure in which a headrest mounting part is provided at the upper end part of an impact-receiving frame which, in a portion in the vicinity of the upper end, is anchored to the upper side pipe part of a seat back frame; and, at the time of a rear collision, the portion which is below the upper side pipe part of the impact-receiving frame is pressed rearward by the seated person, resulting in the upper side pipe part being twisted, and the headrest being automatically moved toward the head side of the seated person (forward). In patent document 2, a vehicle seat structure is disclosed in which a headrest movable frame disposed in a seat back is supported by the seat back frame through a link mechanism; at the time of a rear collision, a wire stretched over the lower part of the headrest movable frame is pressed rearward by the lumber region of an occupant; and this pressing force is changed in direction by the link mechanism, resulting in the headrest being linearly moved upward and forward.
However, in the above-mentioned respective structures, since they are configured such that the impact-receiving frame or the wire is pressed by an occupant, even at a time of normal seating, the occupant will contact it so that an odd sensation will be given to the occupant. Especially, with a seat back structured by stretching a tensile structural element over the frame, this problem becomes more prominent.
On the other hand, in patent document 3, a vehicle seat is disclosed which is structured by stretching a cloth-like member having cushioning ability over a seat back frame including a pair of right and left side frames which is constituted by a side frame upper whose upper end is supported vertically movably with respect to the vehicle body and to which a headrest is fixed, and a side frame lower whose lower end is turnably supported with respect to the vehicle body and whose upper end is turnably connected to the lower end of the side frame upper. With this seat, at the time of a rear collision, the seated person presses the cloth-like member rearward, which causes the side frame upper and the side frame lower to be relatively turned in the direction in which they are brought closer to a straight line when viewed from the side face, thus moving the headrest upward and forward.
However, with this seat, the seat back frame is constituted by the side frame upper and the side frame lower which are turnably connected, but the rearward movement of the upper end of the side frame upper with respect to the vehicle body is restricted, and thus impact energy which causes the occupant to be moved rearward cannot be sufficiently absorbed. Further, with this configuration, since the upper end of the side frame upper is supported with respect to the vehicle body, thus for example, application of the configuration to the front seat, and the like, of a vehicle has been difficult.
Patent Document 1: Japanese Patent Laid-Open Publication No. 2000-185582
Patent Document 2: Japanese Patent Laid-Open Publication No. 2000-325179
Patent Document 3: Japanese Patent Laid-Open Publication No. 2003-25891